1. Field of the Invention
The present invention relates generally to display devices for beam steering and scanning and, more particularly, to flat panel display devices for beam steering and scanning which are electronic in character and which further incorporate logic trees which are designed to steer electromagnetic energy so that both transmission losses and the number of energizing sources of an imaging array are minimized. The devices include a multi-stage imaging array made up of a plurality of stacked logic trees so arranged that each stage of each logic tree includes active steering elements which access twice as many like steering elements and associated passive steering elements in each succeeding stage. The active and passive elements incorporate cholesteric liquid crystal (CLC) elements which are polarization sensitive disposed within them at an angle of 45°. The active elements include variable half-wave retarders which, under control of a programmable pulsed source change the polarization of incident energy on CLC elements and provide a scanned line of electromagnetic energy to the imaging cells disposed at the output of each logic tree. In such an arrangement, array transmission losses are minimized and one source of electromagnetic energy per logic tree is required.
In another arrangement using a similar imaging array, transmission losses are reduced over prior art input arrangements and the number of sources of electromagnetic energy is reduced to one. Using an input logic tree, fed from a single laser and arranged perpendicularly to the array logic trees, the imaging cells of the input logic tree act as inputs to the stacked logic trees of the imaging array. In this way, a scanned line is delivered from each imaging cell of the input logic tree to the first active element of an associated array logic tree. From there, under control of a programmable pulsed generator, portions of the scanned line are directed to the output imaging cells of each of the array logic trees. Two-dimensional images are built up in this way by activating the imaging cells of each array logic tree in succession. Three dimensional images may be obtained using an approach similar to that just described by interleaving stereo displaced images from a 3-D camera at the output imaging cells of an imaging array by activating the first and every other logic tree of an array with one image and the second and every other logic tree with a stereo displaced image. Glasses which respond to a different polarization for each eye are required to produce the 3-D effect.
The present invention also relates to a method of fabricating the above described imaging arrays by slicing stacked alternating layers of insulating material and CLC material. To the extent that a final imaging array requires that each logic tree have twice as many CLC elements per stage as a preceding stage after the first stage, the number of CLC element per stage may doubled by halving the spacing between CLC elements during fabrication. This is accomplished by halving the thickness of the insulation disposed between layers of CLC material after setting the initial spacing between CLC layers which are to be used as the first stage of a logic tree. After producing layers of a given thickness by slicing at a 45° angle, transparent metallic ground planes are formed. Then, using photolithographic and etching techniques, electrodes are formed over every other CLC element. A spacer element is then fixed to the periphery of each layer and the resulting volume is filled with a phase shifter material. The resulting stages are then stacked using as many as required to form an imaging array with a desired number of imaging cells. Stacking the stages, which are slices containing differently spaced CLC elements automatically provides the logic trees which deliver scanned line to the output imaging cells. The method uses mass-production techniques and results in an inexpensive, flat-panel display.
2. Description of the Prior Art
Generally, there are two well-known techniques for the steering and scanning of light beams. One is electromechanical and the other is acousto-optical. Both techniques have severe limitations. One such limitation is that arrangements incorporating these techniques require a large volume due to the small angel through which the light beam can be deflected. Thus, if it is desired to scan a length B, the deflection arrangement has to be positioned a distance, A, providing an A/B ration larger than 1.
All known systems require an A/B ratio larger than 1 and to the extent that the arrangement of the present application can provide A/B ratios which are very much less than 1, the resulting structure may also be characterized as a flat-panel display. In the known scanning approaches, scanning speed is relatively sluggish due to the use of electromechanical or electro-acoustic elements. Because such devices are eliminated in the scanning arrangement of the present application, scanning speeds in the microsecond range are achievable.
U.S. Pat. No. 4,670,744 filed Mar. 14, 1985 and issued Jun. 2, 1987 in the name of T. Buzak incorporates variable optical retarders and liquid crystal chiral cells. This reference takes advantage of the reflective and transmissive characteristics of chiral cells as well as the ability of variable optical retarders to convert one circular polarization to the other circular polarization. However, when a beam containing image information is projected along a given path in which the chiral cells and retarders are disposed, the beam remains in that given path or is retroreflected along the same path. Opposed to this, the arrangements of the present application while they all incorporate the reflection-transmission characteristics of chiral cells, they all incorporate an ability to divert the reflected beams into other paths. To the extent that the Buzak reference seek to provide a three-dimensional display, all the images reflected must lie in a plane parallel to the planes of the chiral cells. Otherwise distortion and degradation of the reflected images would occur due to the required lateral displacement of the chiral cells. In other words, to provide the desired result, no diversion of the beam in the Buzak reference can be tolerated.
U.S. Pat. No. 5,221,982, filed Jul. 5, 1991 and issued on Jun. 22, 1993 to S. M. Faris is entitled Polarizing Wavelength Separator. The patent relates to a polarizing wavelength separating optical element in the form of a flat panel which causes each of a plurality of polychromatic optical beams from a source, entering at one surface and transmitted to another surface, to be converted, with high conversion efficiency, into circularly polarized, spectrally and spatially separated beams. The element is made of a periodic array of cells; each of the latter incorporating a plurality of subcells. One subcell functions as a broadband reflector, while each of the remaining subcells acts as a polarizing, wavelength selective reflector. Each subcell comprises a plurality of layers which are bonded together at their surfaces and are oriented at a 45° angle relative to the horizontal surfaces of the panel. In each subcell, the plurality of layers comprise two cholesteric liquid crystal, CLC films, which reflect at a selected wavelength, at least one optical retarder and clear substrates which provide mechanical support. The thicknesses of the supporting substrates are designed to cause the beams transmitted through the element to be spatially separated by appropriate distances.
In the reference, all the elements utilized in the panel are passive in character which constrain beams of electromagnetic energy into paths which are fixed for all time. In contradistinction to this, the present application, with it electronically controllable retarders, provides paths for electromagnetic energy which can be changed from instant-to-instant taking advantage of both the transmissive and reflective capabilities of CLC elements. The combination of a circularly polarized input with controllable retarders and associated CLC elements in the present invention provides the ability to scan a beam from point to point in a panel-like display or to steer a beam it can emanate from any location on an array of imaging cells. Strictly passive arrays with their fixed paths cannot achieve these results.
U.S. Pat. No. 5,459,591, filed Mar. 9, 1994 and issued Oct. 17, 1995 to S. M. Faris relates to beam steering and scanning devices which utilize an imaging cell which incorporates a solid-state cholesteric liquid crystal (CLC) element, an electronically controlled, variable half-wave retarder and a source of circularly polarized light. The CLC element is disposed to an angle (45°) relative to the path along which light from the source is projected and is designed to reflect, at a given wavelength, one circular polarization of light and transmit the other. Using this characteristic, light of one polarization or the other is presented to the variable retarder and depending on whether or not it is actuated, light is either diverted into another orthogonal path or remains in the original path. If another similar imaging cell is disposed in the orthogonal path, light incident on that cell can also be diverted into yet another path or transmitted along the orthogonal path under control of a half-wave retarders associated with said another imaging cells. By arranging a plurality of imaging cells in the form of an array and accessing each row of the cells of the array with a column of similar imaging cells and by selectively activating half-wave retarders associated with each of the cells, monochromatic or polychromatic light from a single source or multiple sources may be steered to a selected cell and reflected from its associated CLC element or elements. Utilizing successive cells in the array and causing reflection of a modulated beam or beams provides a frame in the manner of the usual TV set which is viewed by the eyes as an integrated picture. Successive frames, of course, provide the usual moving images.